(a) Technical Field
The present invention relates to a light emitting device and a manufacturing method thereof. More particularly, the present invention relates to a light emitting device having a single active layer of a core-shell structure (p-i-n structure) in which intrinsic semiconductor nanocrystals, which serve as exciton combination centers, are uniformly and isotropically distributed around p-type polymer particles, and n-type small molecular particles surround the semiconductor nanocrystals and p-type polymer particles, and that can be driven even by an AC voltage, and a manufacturing method thereof.
(b) Background Art
With rapid progress of electric and electronic technology, electric devices and electronic apparatuses of various functions are under development. For example, various electric devices such as light emitting devices emitting light using an electrical signal, memory devices for storing information, short/long distance wireless communication devices, and sensor devices are under development. Also, displays, or various portable devices such as cellular phones, MP3 players, and digital cameras, information and telecommunication apparatuses are under active development.
The things to be considered with top priority in performing researches to develop electric devices and apply these electric devices to an electronic apparatus of various functions are: miniaturization of the electric devices or electric apparatuses, manufacture of lightweight slim devices or apparatuses, and increase of integration degree and portability to reduce manufacturing costs while improving the reliability of the devices or apparatuses.
The traditional studies on the driving of a general display including a hybrid polymer-quantum dot light emitting device have been mainly focused on devices using a DC voltage. Particularly, a superluminescent diode (SLD) using a quantum dot structure as an active layer has been widely studied.
Also, manufacturing a light emitting diode (LED) using silicon or a compound semiconductor in Group III-Group VI is well known in the art. It has been recently known that when quantum dots (QDs) having a size of about 10 nm or less are dispersed inside an insulator and a voltage is applied to both ends of the insulator, light emission by the quantum dots are generated [K. A. Littau et al., A Luminescent Silicon Nanocrystal Colloid via a High-temperature Aerogel Reaction, J. Phys, Chem, 97, 1224 (1993); P. Mutti et al., Room-temperature visible luminescence from silicon nanocrystals in silicon implemented SiO2, Appl. Phys. Lett., 66 851 (1995); B. O. Dabbousi et al., electroluminescence from close quantum-dot/polymer composites, Appl. Phys. Lett., 66, 1316 (1995)].
In most cases, electroluminescence (EL) is not obtained by manufacturing a device and applying a voltage to it, but a photoluminescence of simply sending light and measuring coming light has been reported. There has been also a report on an LED manufactured by dispersing quantum dots inside a polymer matrix. Here, when the size of a quantum dot is 7.5 nm, light having a wavelength of 920 nm is emitted. As the size of a quantum dot reduces, light having a shorter wavelength is emitted. For example, it has been reported that when the size of a quantum dot is 3.2 nm, light having a wavelength of 660 nm is emitted [K. A. Littau et al., A Luminescent Silicon Nanocrystal Colloid via a High-temperature Aerogel Reaction , J. Phys, Chem, 97, 1224 (1993)]. Recently, various light emitting devices are manufactured by dispersing nano particles in polymers and small molecules, and piling them in a single layer or multiple layer structure.
However, an existing light emitting device having a hybrid polymer-nano particle structure can be driven by only a DC voltage. In a device driven by a DC voltage, the life of the device may reduce or polymers may degrade due to an overcurrent, so that the device may unstably operate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.